Article continues below advertisementKelly Clarkson is heartbroken over the passing of her ex-husband.Brandon Blackstock, who shared two children with the pop star - 11-year-old River and 9-year-old Remington - died of cancer on Thursday, August 7, and a source close to the family said the loss has hit the singer hard.Article continues below advertisementSource: MEGAKelly Clarkson is mourning her ex-husband's passing, a source claimed.